1. Field of the Invention
The present invention generally relates to the presentation of images. More particularly, the present invention relates to a method and apparatus for selecting and displaying a stored digital image of an object, or a portion thereof, corresponding to an image of that object displayed on a film transparency. The present invention is particularly useful in the display and evaluation of medical images, and is especially useful in displaying and evaluating digital or digitized mammographic images.
2. Description of the Prior Art
For decades, mammographic images of breasts have been acquired by exposing a breast to X-rays wherein the varying intensity of X-rays passing through the breast tissue is captured on film to form a mammographic image. In mammography and other medical imaging, medical X-ray transparencies are usually examined by placing them over a light box or illuminator to allow light to pass through portions of the image. Normally, such illuminated transparencies are generally examined or screened by a radiologist who is looking for abnormalities. When an apparent abnormality is found, such as a lesion, it is usually more carefully examined with a magnifying glass, for example.
One example of an illuminator for viewing medical X-ray transparencies may be found in U.S. Pat. No. 5,159,771 wherein X-ray film transparencies are advanced consecutively across a lighted surface in a horizontal direction from a magazine. The device enables such transparencies to be screened relatively rapidly and automatically.
Another example of an illuminator may be found in U.S. Pat. No. 5,430,964. This patent discloses an apparatus for viewing transparencies which masks any display areas not covered by transparencies by generating masks without moving parts and further adapts the luminance level of the image under study and of other display areas to optimal viewing conditions required by the observer such as the radiologist.
In recent years, the use of digital imaging in mammography and other medical imaging has become more widespread due to several advantages that digital imaging has over film based imaging. Digital images do not require an illuminator such as that described above. However, when the entire breast is imaged digitally, for example, the corresponding data files for such images are typically large. The display of such images in their entireties can be very demanding of scarce computer resources. Even for a fast computer system used to display such images, each of the large data files corresponding to an image may take from several seconds up to minutes to retrieve, process and display. In the case where hundreds of images must be evaluated in a relatively short period of time, the several seconds (or minutes in some cases) required per image may be unacceptable. Also, the imaging apparatus used to acquire the image usually has a higher spatial resolution than the spatial resolution of the typical display device, such as a monitor.
While both of the aforementioned illuminators allow rapid evaluation of X-ray film images, these devices lack the digital image enhancement capability such as windowing, contrast stretching, histogram equalization, filtering, edge enhancing, zooming and the like, all of which are useful for the evaluation of medical images, for example. While the digital image display devices have the image enhancement capability, digital display devices currently lack the throughput capability of the aforementioned illuminators.
Thus, there is a need for a device for screening film images, especially medical images, which provides the throughput of the illuminators described above and which also provides the user with the ability to look at selected film images, or portions thereof, with the image enhancing capabilities associated with devices for displaying digital images.